This invention relates to a method and apparatus for abandoning an offshore oil or gas well drilled into the ocean floor and having a plurality of concentric strings of pipe having throughbores and spaced to form an annular space between adjacent pipe strings.
Federal regulations concerning the abandonment of an oil or gas exploration well required that the a determination be made as to whether or not any gas exists in the annular spaces between concentric pipe or casing strings prior to plugging the pipe strings. Prior art and practice on this subject is only concerned with perforating the outer most casing of the well together with a layer of cement outside the casing in order to open up a production formation and allow oil to flow into the well. At times, more than one string of casing in the well was perforated along with the cement surrounding the outermost casing. A perforator was positioned against the wall of the well so as to get the greatest penetration of the bullets or shaped charge shot into the formation through the steel casing and several inches of cement.
It is the object of the present invention to provide a method and apparatus for abandoning a well by perforating a single string of casing of a series of concentric casing strings or pipe strings within a well without damaging or perforating the next adjacent string of casing, and subsequently testing for the presence of gas trapped between casings prior to plugging each casing with a concrete plug.